1. Field of the Invention
The present invention generally relates to injecting material in the cells by using air pressure.
2. Description of the Related Art
In the field of new drug designing, a microinjection device is used for injecting a solution (usually a medicinal solution) into a cell. FIG. 6 is an example of a conventional device. As shown in the diagram, reference numeral 1 denotes a positive pressure pump, and reference numeral 2 denotes a negative pressure pump. Reference numeral 3 denotes a regulator that is connected to the positive pressure pump 1 and the negative pressure pump 2 for keeping constant the internal pressures thereof.
Reference numeral 4 denotes a capillary that discharges a solution into a cell due to the pressure from the regulator 3. The capillary 4 is similar to an injection syringe, and has a fine needle at its tip. The internal diameter of the tip is 0.5 μm and the external diameter is 1 μm. Reference numeral 6 denotes a tube that transmits the pressure from the regulator 3 to the capillary 4, and reference numeral 5 denotes a pressure sensor which is located in the middle of the tube 6.
The pressure detected by the pressure sensor 5 is output to the regulator 3, and the regulator 3 adjusts the internal pressure so that the pressure detected by the pressure sensor 5 is maintained constant. Otherwise, it is possible to arrange the pressure sensor inside the regulator 3 and adjust the internal pressure so as to maintain constant output from the pressure sensor. Electric voltage is input to the regulator 3 as a control signal, and the regulator 3 generates a pressure that is proportional to the input electric voltage.
The needle attached to the tip of the capillary 4 is filled with the solution. Pressure applied by the regulator 3 thrusts a cylinder of the capillary 4 whereby the solution is discharged (injected) into the cell. The cell is observed for a change that occurs after injection of the solution. When the pressure inside the regulator 3 is to be brought back to the atmospheric pressure, air is pulled out from the regulator 3 by the negative pressure pump 2 whereby the pressure inside the regulator 3 is quickly brought back to the atmospheric pressure.
FIG. 7 depicts a pressure response curve of the conventional device. A horizontal axis indicates time and a vertical axis indicates pressure. Initially, the pressure is maintained to reverse flow preventing pressure. After time T1 is elapsed, the pressure reaches up to an injection pressure, and the capillary 4 injects the solution into the cell. The state that the capillary 4 is injected into the cell continues for a predetermined period after which the pressure lowers gradually. The injecting operation stops when the pressure reaches the reverse flow preventing pressure.
The conventional device can be used in a gene delivery device. In the gene delivery device, cells that flow through a micro fluid channel are observed by using a cell observing device, cells are trapped one by one with a cell trapping device, and genetic material and medicinal solutions are discharged into the cells by using a gene delivering micro needle (for example, see Japanese Patent Application Laid-Open No. 2004-166653). Furthermore, a microinjection apparatus has, at its tip, a micro instrument that is connected to a micro syringe, which is filled with the solution. When a male screw is rotated to move a plunger, into the micro syringe, the solution is discharged from the micro instrument (for example, see Japanese Patent Application Laid-Open No. H03-119989).
A microinjecting method of the microinjection apparatus involves filling predetermined volume of a solution in an extra fine capillary, with a tip that is of μ m order, injecting the solution into the cell by pressurizing the capillary, and observing the response. In this process, it is necessary to control sequentially switching of the pressure between a pressure necessary for discharging the solution in the cell and a pressure necessary for preventing reverse flow of the solution into the capillary.
However, the conventional microinjection device, which has the structure shown in FIG. 6, does not take into account the pressure transient response. Therefore, when trace quantity of solution of pl (picolitre) order is to be discharged through injections such as injections into animal cells, if the delivery time is lowered to less than 1 second for speeding a discharge cycle, the set pressure and the set time deviate from the actual response, and adjustment of discharging volume of the solution is difficult.
Therefore, on the conventional microinjection apparatus, an experienced operator would adjust the pressure and the time for applying the pressure while taking into account swelling of the cell when injecting the solution into the cell. However, in this method, it is unclear whether a constant amount of material is discharged into the cell.